A carbon fiber composite material has high specific strength and specific rigidity and is light in weight, so that it is valued as an extremely excellent material in various fields. Hitherto, in joining a thermosetting carbon fiber composite material using a thermosetting resin as a matrix to a different kind of a material, particularly a metal, there have been employed joining using a bolt and a nut, a rivet or the like that is mechanical joining or joining using an adhesive. The mechanical joining with a bolt, a nut or the like generally involves an increase in weight and also particularly, there is a concern that in a composite material, stress is concentrated in a joining point, and in the worst case, fracture continuously proceeds starting from the first stress concentrated point. In the joining using an adhesive, it is generally necessary to secure an adhesive layer having a certain thickness in order to secure strength. Particularly, in the case of joining a large-sized member, a considerably amount of the adhesive is required. As a result, there is a concern for a great increase in weight of the resulting member. Furthermore, there is a problem that joining strength thereof is not always sufficient with only the adhesive. Additionally, in the joining with the adhesive, since much time is generally required until practical joining strength is attained from joining, an aging step must be taken into consideration after the joining.
On the other hand, in a carbon fiber composite material using a thermoplastic resin as a matrix (hereinafter sometimes referred to as a “thermoplastic carbon fiber composite material” or simply a “composite material”), materials are joined to each other by welding in a range that the thermoplastic resin is compatible, and joining strength comparable to a joined body of the matrix resin itself can be expected. However, there are many cases that the joining of the matrix resin to a metal by welding (fusing) is difficult even in the case of the thermoplastic carbon fiber composite material.
To weld the thermoplastic carbon fiber composite material to a metal, it is required that the thermoplastic resin itself used as a matrix can weld to the metal. Patent Document 1 describes that a metal and a resin are joined by welding. Specifically, there is described that the both can be joined due to an anchor effect by injection-molding a resin to an aluminum material whose surface is made finely porous. Moreover, Patent Documents 2 to 6 describe that a resin and a metal are joined by applying a certain treatment to a metal surface.
Furthermore, with regard to a thermosetting carbon fiber composite material containing a thermosetting resin as a matrix, Patent Document 7 describes a joining method with arranging an intermediate resin layer having an affinity with both a metal and the composite material.